Clear images and excellent print quality could have been obtained by technological development in ink jet color printers which form color hard copies at high speed. On the other hand, in order to further improve print quality, chroma, appearance, and images, recording materials having higher levels of properties have been required. In particular, with improvements in printing speed, resolution, chroma, and the like, recording materials have been required to have higher characteristics than usual, such as an ink quick drying property, high-absorption capacity, control of ink dot diameter and blurring, surface gloss, and the like.
Ink jet recording materials including paper as a base material have the problem that contact, with water causes a phenomenon referred to as “cockring” in which the base material waves, or a tear in the base material, thereby worsening an appearance. In order to resolve the problem, it has been proposed that printing is performed on an ink jet recording medium including a plastic film used as a base material, and an ink-receiving layer provided on the plastic film (refer to, for example, Patent Literatures 1 to 4). Such a medium is excellent in water resistance and can also be used for outdoor advertisement and posters, labels, wallpaper, and the like. However, a surface of the plastic film in contact with an ink-receiving agent has low adhesion to the ink-receiving agent, and thus a surface treatment process is usually necessary for forming a layer referred to as an anchor layer, a primer layer, an undercoat layer, an adhesive layer, or the like on the surface of the plastic film. The surface treatment, process leads to not only an increase in cost but also an increase of one step as compared with a case without such treatment, thereby increasing the time required for production. Further, when the surface treatment is performed by applying a coating material containing a solvent, a step of removing the contained solvent is required, and when the solvent is an organic solvent, load on the environment, is increased.
As a method for resolving the above-described problems, an ink jet image-receiving sheet is disclosed, in which a thermoplastic resin film having a Laminated structure including two or more layers is used as a base material and is directly coated with an ink-receiving agent (for example, refer to Patent Literature 5). However, the sheet specifically provided in Patent Literature 5 has a surface composed of high-density polyethylene, and thus cissing may occur in the ink-receiving agent to cause difficulty in clean print finishing. Also, the sheet has the problem of peeling of a print portion due to change with time in adhesion between the receiving agent and the base (film).
Further, from the viewpoint of avoiding contamination of contents, printing on packaging materials has been performed by a simple method in which an ink is printed only on a surface side of a material to be printed, and an ink is not printed on a back side in contact with the contents. This method is called a “surface printing method”. However, in the surface printing method, print fading or dropout may occur due to impact by friction or the like to impair appearances, and during heat sealing for packaging, an ink may be removed by a sealing bar to cause peeling of print, and contamination of a packaging machine, and also in a packaging material having an ink-receiving layer, the ink-receiving layer may be cracked to cause defects in an appearance. Known methods for preventing these problems include lamination of a protective layer (film) on an image surface of a printed material, and so-called over-coating treatment of coating with a coating agent, and these methods are used according to applications of the formed printed materials (refer to, for example, Patent Literatures 6 and 7). However, the over-coating treatment causes peeling or blurring on a print, surface, or the like during the work unless adhesion between the plastic film and the receiving agent is secured, not leading to fundamental resolution of the problems.